Centrifugal impact rock crushing machines, also known as vertical shaft impact crushers, operate to crush rock by propelling it at high speeds against an anvil, or against other rock which has accumulated inside the crushing chamber. In such machines larger rock material is fed through a vertical feed tube onto the center of a rotating table or enclosed rotor having a series of impeller shoes which accelerate and sling the material radially outwardly at a high velocity against stationary wear-resistant anvils spaced around the rotating table. The force of the rock hitting the anvils causes the rock to break along its crystalline planes to form an aggregate of more or less uniform size.
In impact crushers heretofore devised excessive wear of the impeller shoes become a difficult problem due to the stresses and friction created by the rock as it is forced to slide over the working face on one side of each impeller shoe. Such wear made it necessary to stop the crusher machines more often to replace worn out shoes, thereby reducing overall production efficiency.
A significant aspect of the wear problem on standard impeller shoes heretofore devised was that the wear pattern on the impeller shoe face was not uniform. An example of a prior art impeller shoe is shown in U.S Pat. No. 4,174,814. with such prior art impeller shoes, the working face across which the rock moved was a single planar surface. In use, wear or erosion of metal on this planar surface occurred at a faster rate at its thick end, resulting in a decrease in the face angle of the shoe with respect to a radius of its rotating table. This decrease in face angle also had the undesirable effect of decreasing crushing efficiency and production.
Accordingly, one principal object of the invention is to provide an improved impeller shoe for an impact crusher that will wear more evenly and uniformly along its front aggregate contacting or working face and thus have a longer useful life.
Another object of the invention is to provide an improved impeller shoe for an impact crusher whose working face angle will remain substantially the same as it normally wear during its useful life.
Still another object of the invention is to provide an impeller shoe for an impact crusher which will have greater wearability and will maintain crushing productivity during its life.